Solr search doesn't show contents if the attchment is .doc or .pdf

Not quite sure should I ask Foswiki or Solr search engine?

We use solr search engine with Foswiki. In the search, if the attachment is .doc or .pdf, the contents is showed as non-recognised like below, but if the attachme is .txt or .xlsx, it's fine. Any advice is appreciated.

Password-protected office files may fail as well. These are only readable with a user interaction, i.e. not full-text-indexable.

One you changed these settings go to <foswiki-dir>/working/work_areas/SolrPlugin/ and delete all subdirectiries in there.
These are the cached stringified versions of your office documents. Once you've deleted them your next indexing run will extract
the office docs using the newer stringifier settings.

There is a testing tool available as well: see <foswiki-dir>/tools/stringify <file-name> that you can use to fire up stringifier on
the commandline.